Sending unit pinout

[Marvelicious]

There are 4 sensors on my 82 SD that share a harness - one on the thermostat housing, one on the back of the intake, one about mid-head by the glow plugs, and one down below the oil filter. I need to know what they all do and where they go, or more importantly, which one corresponds to which pin on the connector on the inner fender.

What happened is... I did a mystery oil soak and a valve adjustment last weekend. When I was taking the wires off the glow plugs, I noticed that the wires were VERY stiff, complete with cracking insulation, and the sensor wires on the same harness had the same problem - the one for the sensor on the thermostat housing came apart in my hand. So I decided to go ahead and rebuild that whole harness, use some of that corrugated wire protector, etc... Well, I had just taken the sensor connector apart when it occured to me that I had better make a map. Well, I accidentally dropped it, and the ends popped out of the connector. Now I don't know which is which. I don't know when I'm going to learn to use that digital camera like I should.

[Marvelicious]

Well, since no one had an answer, I'll post what I did in case anyone else ever has the problem.

I hooked it up as my best guess, which turned out wrong as my oil pressure was pegged before I started the car... After swapping the wire at the head and the wire at the oil filter, that gauge worked correctly. So, as I have it now:

Pin 1 - Thermostat housing. This is the sensor that people use for the afterglow mod.
Pin 2 - Bottom of the oil filter. Pretty sure this is the oil pressure sender, since the gauge works right now. This is the one that I'm confident is in the correct position.
Pin 3 - Back of the intake manifold. Can someone tell me what this sensor does?
Pin 4 - Center of head. I assume this is the temp sender. I'll keep my eye on the gauge to try and confirm that I've got the right pin. Seems like it could be right so far...

So, can anyone confirm or deny any of this, or at least tell me what that intake sensor is for so I can educate my guesses a little better? I think I've got it right, but a little confirmation would go a long way towards my piece of mind.

[Marvelicious]

Its kind of liberating talking to myself. Now I see why crazy people do it...

[JiveTurkey]

I'll take a look when I get a chance tomorrow to confirm or deny this information

[Marvelicious]

Awesome. I'm pretty sure about pin 2 and 4 now. Oil pressure and engine temp are behaving right now. Really, if I just knew what that sensor on the back of the intake does, or just confirm that it is supposed to be pin 3.

I really do appreciate the help.

[charmalu]

The sensor on the intake is a pressure switch. too much boost & it sends a sig to the switch over valve. the SOV has the boost line from the intake manfold, then to the ALDA.

Charlie

[Marvelicious]

Aha, gotcha. I'll have to see if I can't chase either pin back to the switchover valve then. My switchover was bypassed when I bought the rig - just another little detail I've fixed - with a piece of hose loosely holding the two lines together. If I understand the system correctly, the more pressure the ALDA see's through this line, the more fuel it lets through, so a leaky connection would kill power. So whoever did that, instead of improving power, effectively had overboost protection kicked in all the time. No wonder it was gutless at first.

Edit, come to think of it, if I had this and the A/C temp switch sensor reversed, the switchover valve would activate as soon as the car hit 40C. I'd lose power when the car warmed up. I'm sure thats not going on, so I think I'm good now. Thanks for the help.

[charmalu]

The switchover valve is a protection for the engine if there is too much boost from the turbo.

It has been known, some connect the boost line from the manifold to the ALDA, by passing the SOV.


Charlie

[Marvelicious]

Yeah, thats how it was, but the two vacuum lines were put together with a section of hose that was too loose to hold pressure, so instead of acting like there was no valve (which was the intent) it was acting like the lines were just unhooked, or the valve was always venting to atmosphere.

[JiveTurkey]

Sorry I haven't been able to respond yet, I'm down and out with one hell of a flu.

[Marvelicious]

Don't worry about it, I'm pretty confident I've got it right now. Knowing that sensor was for the switchover valve was the final piece of the puzzle for confirmation. Worry about getting well instead!